VI SENSATION Two pieces of the puzzle The

VI. SENSATION

Two pieces of the puzzle. . • The nervous system’s job is to coordinate us with our environment. – Electric-chemical process • We are exposed to an enormous amount of stimuli. – To deal with this, our perceptions can be biased.

A. What is sensation? • How does physical energy from the environment get encoded as neural signals? • 1. Sensation: process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

A. What is sensation? • 2. Sensation vs. Perception • Sensation is not all we require to make sense of world (“to see the bear”) • Sensation: detecting physical energy. . • Perception: How we select, organize, and interpret the information we sense. – Active process, involves imposing order on stimuli – Sensation provides “raw” information (stimuli) that is selected, organized, etc.

B. Basics of Sensation: • • • 1. 5 senses Seeing Hearing Smelling Tasting Touching

B. Basics of Sensation: Sensation involves converting one type of energy into another. - Energy from environment – to neural impulses. • i. External Stimulus (energy) – big, furry, smelly bear • ii. Stimulus takes different energy forms. . . – • iii. That energy interpreted by receptors. – • see bear: light waves. . . see bear: light waves received by photoreceptors in retina iv. Convert that energy into form brain can understand. 2. Transduction: Stimulus is converted into neural impulses

C. What do we sense/detect from the environment? • We do not detect all of the stimuli that are present. Examples? • Senses are limited or restricted. • 1. Absolute Threshold: The minimum stimulation necessary to detect a particular stimulus. (usually 50% of time)

C. What do we sense from the environment? • How do we determine absolute threshold? • 2. Signal Detection Theory: Used to predict how & when we will detect a stimulus. Considers: – Strength of signal Absolute thresholds vary – not inherent to the stimulus. – Situational differences (expectations, motivation, fatigue) – Individual differences (experience)

C. What do we sense from the environment? • 3. Sensing the difference between 2 stimuli: • Difference threshold (just noticeable difference): Minimum difference a person can detect between any two stimuli (50% of the time) – How to detect the JND? • right or wrong • adjustment – The JND increases with the magnitude of the stimulus.

C. What do we sense from the environment? • 4. Can we ever detect stimuli that are below threshold? Subliminal: below one’s absolute threshold for conscious awareness. • How do we test for this? – Yes – can detect stimuli under threshold. – Yes – can have subtle, fleeting influence on thinking. – No – does not have powerful, enduring effect on behavior.

C. What do we sense from the environment? • 4. What else influences our sensitivity to stimuli? • Sensory Adaptation: diminishing sensitivity to an unchanged stimulus. - after constant exposure to a stimulus, our nerve cells fire less frequently. • But. . .

• Why? • Our eyes are always quivering just enough to maintain stimulation of neurons.

D. VISION • • • Review the basic process: Stimulus input (“bear” or beautiful sunset) Input as light waves Received by receptors in eye. Light waves transformed into neural information – impulses (transduction). • Messages go to brain to be organized/interpreted - to where in brain?

D. VISION • 1. What is the stimulus input? a. Light waves or energy. - Pulses of electromagnetic energy that our visual system experiences as color. - Do we see all possible light waves?

D. VISION • 1. What is the stimulus input? What determines the characteristics of the colors we see? – a. Wavelength: Distance from one wave peak to another. – Determines “hue” or color. – b. Amplitude: Wave height. – Determines amount of energy in light wave or intensity/brightness.

D. VISION • 2. The process of light energy becoming vision. a. Structure of the eye – key are the receptors.

D. VISION • a. Important Structures: • cornea: transparent protector. • pupil: adjustable opening, determines how much light is let into eye. • lens: focuses incoming rays into an image on retina. • retina: light sensitive tissue - receptors.

D. VISION • b. Accommodation Process by which lens changes shape to focus the image of objects on retina. c. Receptors in retina - When image focused onto retina by lens: upside down. - Key to vision: light energy neural impulses Light strikes receptors in retina produces chemical changes (photopigments that break down) trigger neural impulses.

D. VISION • c. Receptors (2 types): Rods: located in peripheral area of retina. – Highly sensitive to light. – Enables black and white vision. Cones: located in fovea (retina’s central point of focus). – Each cone has cell that relays messages directly to visual cortex – Detects fine detail from light energy. – Enables us to see color.

Retina processes some info before gets to brain (encodes and analyzes it) Chemical reaction – activates bipolar cells – eventually activates ganglion cells that make up the optic nerve. Info. sent to brain through optic nerve brain rearranges image to right side-up.

D. VISION • When info. reaches visual cortex, processed by feature detectors. • d. Feature Detectors: Neurons in brain that respond to specific features of the stimulus (shape, angles, movement). • Importance of “brain” in vision: – “parallel processor” • e. Comparing the vision process to other senses. . .

D. Vision • 3. Color Vision • Light rays themselves aren’t “colored” • Color of an object is the wavelength “rejected” or reflected (versus the others that are absorbed) • a. Young-Helmotz Trichomatic Theory • Retina - cones that are sensitive to 3 colors: – – red, green, blue each contain different photopigment fires differently depending on wavelength struck by relationship to colorblindness?

D. Vision • • 3. Color Vision After-images – why? b. Opponent-Process Theory Neurons are sensitive to “pair of opponent” colors: – red/green, blue/yellow, black/white – stare at green – remove green stimulus – cell is fatigued – leaves only “opponent” color part of cell to fire – red – also explains why color blind people can see yellow

D. VISION • 4. Why do some people have poor vision? a. Acuity: sharpness of vision. Poor vision: Caused by small distortions in shape of eye ball. b. Nearsightedness: eyeball is longer than normal in relation to lens. b. Farsightedness: eyeball is shorter than normal in relation to lens.

• Sensation: - haven’t touched on organizing/interpreting that material (perception) - “raw” material for perception - started at “entry level”, data driven “bottom-up processing” • Perception: “top-down processing” - concept driven, use preexisting knowledge to interpret information.

From yesterday. . . • Sensation: Detecting physical energy from the environment – then converting it to neural impulses. • With perception – allows us to communicate and react to our environment. • Both situational and individual variables determine what we detect. • Important to know what stimuli we can detect, and if we can detect differences between stimuli.